Modulation of the Coordination Environment of Copper for Stable CO2 Electroreduction with Tunable Selectivity.

Manipulating the product selectivity of an electrochemical CO2 reduction reaction (CO2RR) is challenging due to the unclear and uncontrollable active sites. Here, we report stable CO2RR operation with tunable product selectivity over a family of molecule-modulated copper catalysts. The coordination environment of Cu in catalysts is modulated by an imidazole-based molecule via different synthetic routes. Various carbonaceous products ranging from carbon monoxide, methane, and ethylene were selectively produced via, respectively, tuning the coordination environment of copper atoms from Cu-N, Cu-C, and Cu-Cu. Density functional theory (DFT) calculations reveal that the Cu-N sites weaken the adsorption energy of the *CO intermediate, which is beneficial for CO desorption. The Cu-C and Cu-Cu sites, respectively, facilitate the formation of *OCOH and *(CO)2 intermediates, favoring the CH4 and C2H4 pathways. This work provides a stable and simple model system for studying the influence of coordination elements on the product selectivity of CO2RR.

A tandem effect of atomically isolated copper-nitrogen sites and copper clusters enhances CO2 electroreduction to ethylene.

Direct electrochemical conversion of CO2 to C2H4 with high selectivity is highly desirable for lowering CO2 emissions. However, limited by the slow *CO dimerization step at a single active site, it is difficult for current electrocatalysts to further improve the selectivity toward C2H4. Here we report a tandem catalyst PDI-Cu/Cu with Cu-N sites and Cu clusters, synthesized by uniformly dispersing Cu clusters on a coordination polymer PDI-Cu, which has atomically isolated Cu-N sites. This tandem catalyst, which has an optimal content of Cu clusters, shows more than 2 times the enhancement in C2H4 production compared with that of the non-tandem catalyst PDI/Cu. Density functional theory (DFT) calculations support the tandem reaction mechanism, where Cu-N sites first reduce CO2 into highly concentrated CO and then the CO migrates to the surfaces of Cu clusters for further conversion into C2H4, decoupling the complex C2H4 generation pathway at single active sites into a two-step tandem reaction. This work offers a rational approach to design electrocatalysts for further boosting the selectivity of the CO2RR to C2+ products via a tandem route.